This invention relates to a crucible apparatus which can be used for solidifying a molten material and a method of solidifying a molten material using the apparatus. In particular, this invention relates to a crucible apparatus and solidifying method which are ideal for solidification of molten silicon obtained by melting scrap silicon and evaporating impurities in the silicon.
It is desirable to reuse scrap silicon which is formed when manufacturing semiconductor silicon. However, in some cases, scrap silicon contains impurities (dopants), so in order to reuse such scrap silicon, it is necessary to first remove the impurities and increase the purity of the silicon. Techniques for vacuum refining of scrap silicon using an electron beam have been developed in order to accomplish these tasks. In vacuum refining, lumps of silicon which are obtained by crushing of scrap silicon are irradiated with an electron beam and melted to evaporate impurities contained in the scrap silicon and increase the purity of the silicon. The molten silicon is then solidified in a crucible to obtain a high purity silicon ingot.
In the above-described method of vacuum refining of silicon, a one-piece quartz crucible like that described in Japanese Published Unexamined Patent Application 2002-226291 is typically used. However, in order to remove solidified silicon from such a crucible, it is necessary to destroy the crucible, so the crucible cannot be reused. A quartz crucible is extremely expensive, so the need to destroy the crucible increases the cost of refining scrap silicon.